Deteriorated FDCs in aged p50-/- mice correlates with reduced IgM-IC localization A. 2 month and 6 month old B6 mice and 6 month old p50-/- mice were injected with IgM-IC and analyzed by IH for IgM-IC localization 16 h later. IgM-IC were present on FDCs in 2 and 6 month B6 mice (see arrows), but were not deposited onto FDCs in p50-/- mice. B. Intense CD21 staining (designated by arrows) was less visible in the spleens of p50-/- mice, indicating that FDC networks were poorly developed in these mice. This suggests that reduced IgM-IC localization may be attributed to the loss of functional FDC networks in p50-/- mice. The magnifications noted refer to the objective used, not the absolute magnification.